The present invention relates generally to methods for setting a mask pattern and an illumination condition optimal to the mask pattern, and more particularly to a method for setting a mask pattern and its illumination condition suitable for an exposure method for illuminating a mask that arranges a desired pattern and an auxiliary pattern or dummy pattern (these terms are used interchangeably in this application) smaller than the desired pattern, using plural kinds of light so as to resolve the desired pattern without resolving the auxiliary pattern on a target via a projection optical system.
A projection exposure apparatus has been used for the photolithography to manufacture devices such as ICs, LSIs, and liquid crystal panels. The projection exposure apparatus has generally shortened an exposure wavelength and/or enlarged a numerical aperture (NA) of its projection optical system to achieve high resolution.
Although the resolution generally improves with the shorter exposure wavelength and the larger NA, the projection exposure apparatus has, from its nature, patterns that are easily resolved and patterns that are hard to be resolved. Generally speaking, a line and space pattern (“L/S pattern” hereinafter) is more easily resolved than a contact hole pattern (“C/H pattern” hereinafter), and thus the C/H pattern is usually made wider than the L/S pattern for use with semiconductor chips. Therefore, there has been a problem to manufacture a minute C/H pattern in the fine lithography.
While an attempt to insert a dummy pattern into a desired C/H pattern has been proposed to change the pattern transfer performance, the dummy pattern has been inserted mainly to improve the depth of focus. In addition, an illumination system has conventionally used an annular or quadrupole shape as an effective light source shape for this case.
The instant inventors have discovered that the way of inserting the dummy C/H pattern would change an imaging state of a desired C/H pattern. The instant inventors have also discovered an insertion rule of a dummy C/H pattern based on a size, period, arrangement of a desired C/H pattern, etc. The instant inventors further discovered that a certain insertion method of a dummy pattern would improve not only the depth of focus but also the resolution, and that the optimal illumination system is neither the annular illumination nor the quadrupole illumination. In particular, according to the experiences of the instant inventors, the quadrupole illumination is seldom useful when k1 is 0.25×√2 or smaller, where k1 corresponds to a half pitch of a mask pattern that arranges the dummy pattern. Here, k1 is a factor expressed by k1=R·NA/λ, where R is the resolution, NA is a numerical aperture, and λ is a wavelength of an exposure light source. In addition, the prior art has inserted a dummy pattern into a desired pattern only when the desired pattern has a certain period. However, desired patterns do not always have certain periods in an actual mask pattern, and thus the prior art has limited applicability. The instant inventors have also discovered that a desired pattern on a mask is sometimes not successfully reproduced even when a dummy C/H pattern follows the insertion rule and the illumination system is set to be suitable for the mask pattern. In this case, the desired pattern should be corrected.